newbie question

[nagplbob]

I bought a used system for a low budget build ... when all is done, I'll have $350 in this build, including the used Dell

my question is re: the difference in prices on ebay for seemingly the same items ... I am registered on ebay, tho I've never bought anything off ebay

this from a large-ish dealer on ebay, thousands of sales, 99% rating, several different listings of the same card, with same specs listed ... ATI Radeon 9800 Pro, AGP, 256 MB DDRRam, Eightparallel rendering pipelines, Fourparallel geometry engines, 128-bitDDR memory, interface AGP 8Xsupport, AGP8X (0.8v), 4X (1.5V) or Universal AGP 3.0 bus configuration (8X/4X)

all are listed as new, in the box, OEM replacement, 12 month warranty

the listed specs are the same, and with no bids, the same item prices vary from $0.10 to $0.40, to $12, to free shipping, and even when paying for shipping, the price is usually a couple dollars cheaper than the buy it now, free shipping price ???

I don't get it, what am I missing, why the price differences, what should I be wary of ?

here's my build, the parts I've added/replaced, it is a 2nd computer that should do what I need:

Dell Dimension 4400 - used, working, XP Pro, SP3
TrendNet NIC
Crucial DDR memory - 2 sticks 512kb
PC Power & Cooling 500W psu
Intel 2.4 processor and fan/heat sink
Radeon 9800 Pro - estimated $60-$70
the psu is overkill, but I plan on using it for a higher end build in the future

I know what I want, but don't want to end up with the wrong item ... the price differences scare me when the listed specs are exactly the same ... thanks for enlightening me